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gas exchange system in fish (gills (organs of gas exchange (large surface…
gas exchange system in fish
specialised respiratory systems
overcome viscosity and density of water and lower oxygen content
diffusion in water is slower than in air
fish are big, active animals
cells have a high oxygen demand
small SA:V ratio
diffusion is not enough to supply inner cells with oxygen needed
scaly outer covering does not allow gas exchange
take oxygen from water and release carbon dioxide into water
gills
contained in gill cavity
covered by protective operculum - bony flap
to allow efficient gas exchange - maintain flow of water over gills even when not moving
gills
maintain flow of water in one direction over gills
organs of gas exchange
large surface area
good blood supply
thin layers
when fish swim - maintain a current of water flow over gills by opening mouth and operculum
when movement stops - flow of water stops
ram ventilation - ram water past gills e.g. sharks and rays
gill arch
support structure of gills
gill filaments
occur in large stacks (gill plates) - need flow of water to keep them apart
exposes large surface area needed for gas exchange
gill lamellae
rich blood supply
large surface area
main site of gas exchange
blood vessel carries blood leaving gills in opposite direction to incoming water
maintains steep concentration gradient
water flow over gills
mouth opens
buccal cavity lowered
volume in buccal cavity increased
pressure in cavity drops
water moves into buccal cavity
opercular valve is shut
opercular cavity expands
pressure in opercular cavity drops
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mouth closes
operculum opens
sides of opercular cavity move inwards
pressure in opercular cavity increases
water is forced over gills and out of operculum
floor of buccal cavity moves up
flow of water over gills is maintained
adaptations for effective gas exchange
large surface area for diffusion
rich blood supply to maintain steep concentration gradient for diffusion
thin layers - short diffusion distances
tips of adjacent gill filaments overlap
increases resistance to flow of water over gill surfaces
slows down movement of water
more time for gas exchange to take place
water moving over gills and blood in gill filaments flow in different directions
steep concentration gradient is needed for fast and efficient diffusion to take place
countercurrent exchange system
steeper concentration gradients maintained than if blood and water flowed in same direction (parallel system)
more gas exchange takes place
removes 80% of oxygen from water flowing over them
parallel system removes 50% of oxygen only